Magnetic apparatus

ABSTRACT

An imaging apparatus for imaging a sample includes a magnetic apparatus that defines a sample volume that is large enough to accommodate the sample to be imaged, and one or more magnetically manipulatable materials within the sample. The magnetic apparatus includes a magnet that is configured to create a magnetic field having a magnitude B in the sample Each magnetically manipulatable material is a material that exhibits a transition between a first magnetic state and a second magnetic state in response to a change in a property associated with the sample while the magnetic field having the magnitude B is maintained in the sample.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/482,072, filed Apr. 5, 2017 and to U.S. Provisional Application No.62/632,201, filed Feb. 19, 2018, both of which are incorporated hereinby reference in their entirety.

TECHNICAL FIELD

The disclosed subject matter relates to magnetic apparatuses that employmagnetically manipulatable materials within a sample.

BACKGROUND

Magnetic apparatuses can be used for imaging. For example, a magneticimaging apparatus such as a magnetic resonance imaging (MM) apparatususes magnetic fields to image or visualize internal structures ofsamples such as a physiological or biological sample. An MRI apparatuscan use labels in the sample to help imaging.

SUMMARY

In some general aspects, an imaging apparatus is configured to image asample. The apparatus includes a magnetic apparatus that defines asample volume that is large enough to accommodate the sample to beimaged, and one or more magnetically manipulatable materials within thesample. The magnetic apparatus includes a magnet that is configured tocreate a magnetic field having a magnitude B in the sample. Eachmagnetically manipulatable material is a material that exhibits atransition between a first magnetic state and a second magnetic state inresponse to a change in a property associated with the sample while themagnetic field having the magnitude B is maintained in the sample.

Implementations can include one or more of the following features. Forexample, the imaging apparatus can also include an energy supplyconnected to the magnet. The magnet can include electrically conductivewire coils through which current from the energy supply is passed, andthe energy supply can provide a DC current supplied to the wire coils.The magnet can be a superconducting magnet.

The magnetic field magnitude B can be greater than 0.5 Tesla or in arange of 1-20 Tesla.

The first magnetic state can be an antiferromagnetic state or aparamagnetic state, and the second magnetic state can be a ferromagneticstate or a ferrimagnetic state.

The magnetically manipulatable material can exhibit the transition whilethe temperature in the sample is between 270 and 370 K.

The property associated with the sample can be a temperature, and thetransition can occur in response to a change in temperature less than 20K.

The imaging apparatus can include a sample property scanning systemconfigured to change the property of the sample while the magnetic fieldhaving magnitude B is maintained in the sample. The sample propertyscanning system can include one or more of: a temperature scanningsystem for changing a temperature of the sample; and a magnetic scanningsystem for changing a magnetic field of the sample. The temperaturescanning system can include an apparatus thermally connected to thesample. The thermally connected apparatus can include an inductionheater that operates at either a medium frequency or a radio frequencyrange and includes a controller, and a heat inductor.

The property associated with the sample can be a magnetic field, and thetransition can occur in response to a change in a magnitude of amagnetic field that is substantially smaller than the magnitude B.

The magnetic apparatus can be a magnetic resonance imaging apparatus.The imaging apparatus can include one or more gradient magnetsconfigured to produce a variable magnetic field that has a magnitude Ythat is substantially smaller than the magnitude B; and anelectromagnetic source configured to produce a varying electromagneticfield having a magnetic field magnitude that is substantially smallerthan the magnitude B.

The imaging apparatus can also include a delivery apparatus configuredto transport the magnetically manipulatable material into the sample.

The magnetically manipulatable material can be a magnetocaloricmaterial. The magnetically manipulatable material can be a materialselected from the group consisting of iron-rhodium, alloys ofiron-rhodium, alloys of manganese arsenide, Heusler alloys, and alloysof manganese-iron.

The sample can be a living organism and the sample can therefore be heldat a physiological temperature to maintain the organism in a livingstate.

The imaging apparatus can include a detector that detects a signalproduced as a result of the interaction between the magnetic field andthe sample. The imaging apparatus can include a control system connectedto the magnetic apparatus. The control system can be configured to:receive data output from the detector, the output relating to thedetected signal, analyze the received data, and estimate the sampleproperty based on the analysis. The imaging apparatus can include adisplay. The control system can be configured to create an image of thesample at the display based on the analysis. The detector can detect thesignal produced as a result of the interaction between the magneticfield and the sample by detecting a signal produced by tissue within thesample that is in proximity of the magnetically manipulatable material.The signal produced by tissue within the sample that is in proximity ofthe magnetically manipulatable material can include electromagneticradiation generated from protons within the sample in proximity of themagnetically manipulatable material.

Each magnetically manipulatable material can be in the form of aplurality of spatially-separated particles. The particles can bedispersed throughout at least one region of interest within the sample.The size of the particles can be on the order of the size of cellswithin a sample that is a living organism. The size of the particles canbe on the order of micrometers. Each particle can have a microscopicsize.

The magnetically manipulatable material can remain magneticallyunsaturated while the magnetic field having the magnitude B exists inthe sample.

The one or more magnetically manipulatable materials can include aplurality of magnetically manipulatable materials, with eachmagnetically manipulatable material having a transition that occurs inresponse to a distinct change in the property of the sample.

A first of the magnetically manipulatable materials can have atransition from the first magnetic state to the second magnetic statethat occurs in response to an increase in the sample property. And, asecond of the magnetically manipulatable materials can have a transitionfrom the first magnetic state to the second magnetic state that occursin response to a decrease in the sample property.

A first of the magnetically manipulatable materials can have atransition from the first magnetic state to the second magnetic statethat occurs in response to an increase in the sample property. And, asecond of the magnetically manipulatable materials can have a transitionfrom the second magnetic state to the first magnetic state that occursin response to an increase in the sample property.

A first of the magnetically manipulatable materials can have atransition between the first magnetic state and the second magneticstate that occurs in response to a change in a first sample property.And, a second of the magnetically manipulatable materials can have atransition between the first magnetic state and the second magneticstate that occurs in response to a change in a second sample propertythat is distinct from the first sample property.

The transition from the first magnetic state to the second magneticstate can occur in a first range of values of the property as theproperty is increased. The transition from the second magnetic state tothe first magnetic state can occur in a second range of values of theproperty as the property is decreased. The first range of values isdistinct from the second range of values.

In other general aspects, a method includes: receiving a sample in asample volume defined by a magnetic apparatus; preparing at least onemagnetically manipulatable material within the sample; creating amagnetic field having a magnitude B in the sample; changing a propertyassociated with the sample while maintaining the magnetic field havingthe magnitude B in the sample; and detecting a transition between afirst magnetic state and a second magnetic state of a magneticallymanipulatable material in the sample in response to the changingproperty associated with the sample.

Implementations can include one or more of the following features. Forexample, the method can include supplying energy to the magnet in theform of a DC current.

The magnetic field of magnitude B can be greater than 0.5 Tesla or in arange of 1-20 Tesla.

The first magnetic state can be an antiferromagnetic state or aparamagnetic state, and the second magnetic state can be a ferromagneticstate or a ferrimagnetic state.

The property associated with the sample can be changed while maintainingthe temperature in the sample at a value between 270 and 370 K. Theproperty associated with the sample can be changed by changing atemperature in the sample in a range that is less than 20 K. Theproperty associated with the sample can be changes by changing amagnetic field in the sample in a range that is substantially smallerthan the magnitude B.

The method can include: producing a variable magnetic field that has amagnitude Y that is substantially smaller than the magnitude B; andproducing a varying electromagnetic field having a magnetic fieldmagnitude that is substantially smaller than the magnitude B.

The at least one magnetically manipulatable material can be preparedwithin the sample by transporting the magnetically manipulatablematerial into the sample. The magnetically manipulatable material can betransported into the sample by dispersing the magnetically manipulatablematerial in the form of a plurality of particles throughout at least oneregion of interest within the sample.

The sample can be a living organism, and the method can also includemaintaining a temperature of the sample at a physiological temperatureto maintain the organism in a living state.

The method can include detecting a signal produced as a result of theinteraction between the magnetic field and the sample. The method caninclude: receiving the detected signal produced as a result of theinteraction between the magnetic field and the sample; analyzing thedetected signal; and estimating the sample property based on theanalysis. The method can include creating an image of the sample basedon the analysis.

The signal produced as a result of the interaction between the magneticfield and the sample can be detected by detecting a signal produced bytissue within the sample that is in proximity of the magneticallymanipulatable material. The signal produced as a result of theinteraction between the magnetic field and the sample can be detected bydetecting electromagnetic radiation generated from protons within thesample in proximity of the magnetically manipulatable material.

The at least one magnetically manipulatable material can include aplurality of magnetically manipulatable materials, with eachmagnetically manipulatable material having a transition that occurs inresponse to a distinct change in the property of the sample.

The transition from the first magnetic state to the second magneticstate can occur in a first range of values of the property as theproperty is increased; the transition from the second magnetic state tothe first magnetic state can occur in a second range of values of theproperty as the property is decreased; and the first range of values isdistinct from the second range of values. The transition between thefirst magnetic state and the second magnetic state of the magneticallymanipulatable material in the sample can be detected by: detecting thetransition from the first magnetic state to the second magnetic state asthe property is increased; detecting the transition from the firstmagnetic state to the second magnetic state as the property isdecreased; detecting the transition from the second magnetic state tothe first magnetic state as the property is increased; or detecting thetransition from the second magnetic state to the first magnetic state asthe property is decreased.

In other general aspects, an imaging apparatus includes: a magneticapparatus that defines a sample volume that is large enough toaccommodate a sample to be imaged. The magnetic apparatus includes amagnet that is configured to create a magnetic field having a magnitudeB in the sample. While the magnetic field having a magnitude B ismaintained in the sample, one or more magnetically manipulatablematerials within the sample transition between a first magnetic stateand a second magnetic state.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of an apparatus including a magnetic apparatushaving a magnet and a magnetically manipulatable structure embedded in abody of a sample in the magnet;

FIG. 2 is a block diagram of an implementation of the apparatus of FIG.1 in which the magnetically manipulatable structure includes one or moremagnetically manipulatable materials, each magnetically manipulatablematerial being a material that exhibits a transition between a firstmagnetic state and a second magnetic state in response to a change in aproperty associated with the sample;

FIG. 3A is a graph of a magnetic state M (or magnetic moment) of animplementation of a magnetically manipulatable material that can be inthe magnetically manipulatable structure of FIG. 2 versus the sampleproperty, where the sample property is the temperature T;

FIG. 3B is a graph of a magnetic state M (or magnetic moment) of animplementation of a magnetically manipulatable material that can be inthe magnetically manipulatable structure of FIG. 2 versus the sampleproperty, where the sample property is the temperature T;

FIG. 4 is a graph of a magnetic state M (or magnetic moment) of animplementation of a magnetically manipulatable material that can be inthe magnetically manipulatable structure of FIG. 2 versus the sampleproperty, where the sample property is the magnetic field within thesample;

FIG. 5A is a graph of a magnetic state M (or magnetic moment) of animplementation of a magnetically manipulatable material versus thesample property, where the sample property is the magnetic field withinthe sample;

FIG. 5B is a graph of a magnetic state M (or magnetic moment) of animplementation of a magnetically manipulatable material versus thesample property, where the sample property is the temperature within thesample;

FIG. 6A is a schematic representation of a sample in which themagnetically manipulatable structure includes a plurality of differentmagnetically manipulatable materials;

FIG. 6B is a graph of a magnetic state M (or magnetic moment) of the twomagnetically manipulatable materials of FIG. 6A within the sample versusthe sample property, where the sample property is the magnetic fieldwithin the sample;

FIG. 7A is a graph showing an implementation of a magneticallymanipulatable material that transitions from a magnetic to anon-magnetic state with a rise in temperature;

FIG. 7B is a graph showing an implementation of a magneticallymanipulatable material that transitions from a non-magnetic to amagnetic state with a rise in temperature;

FIG. 8 is a graph of a magnetic state M of the first and the secondmagnetically manipulatable materials of FIGS. 7A and 7B within thesample versus temperature;

FIG. 9 is a block diagram of an implementation of the apparatus of FIG.1 in which the magnetically manipulatable structure is a magnetocaloricactuator that is thermally coupled with a thermally-sensitive biologicalconstruct within the sample;

FIGS. 10A and 10B are schematic illustrations of an implementation inwhich the thermally-sensitive biological construct of FIG. 9 is an ionchannel positioned along a cellular structure of the sample, themagnetocaloric actuator includes a plurality of magneticallymanipulatable materials near the ion channel; and the ion channel has aclosed status (FIG. 10A) or an open status (FIG. 10B);

FIG. 11 is a schematic illustration of an implementation of a samplethat includes a plurality of thermally-sensitive biological constructsand a magnetocaloric actuator associated with each of these biologicalconstructs;

FIG. 12 is a schematic illustration of an implementation of a singlemagnetocaloric actuator having different magnetically manipulatablematerials that are mixed together (but do not interact with each other);

FIG. 13 is a schematic illustration of an implementation of a testapparatus for demonstrating the feasibility of using magnetocaloricmaterials as thermal actuators of temperature-sensitive biologicalconstructs in genetically-modified cells while in a DC magnetic field;

FIG. 14A is a graph of a measurement of the magnetic moment of a 99%purity FeRh structure as a function of temperature in different bias DCmagnetic fields;

FIG. 14B is a graph of a measurement of the magnetic moment of a 99.9%purity FeRh structure as a function of temperature in different bias DCmagnetic fields;

FIG. 15A is a graph of a measurement of the magnetic moment of a 99%purity FeRh structure as a function of varying magnetic field atconstant temperature;

FIG. 15B is a graph of a measurement of the magnetic moment of a 99.9%purity FeRh structure as a function of varying magnetic field atconstant temperature;

FIG. 16 is a block diagram of an implementation of a testing apparatusto demonstrate operation of the apparatus of FIGS. 1, 2, and 9 in whicha disk of FeRh is embedded in agarose next to a thermometer 1681;

FIGS. 17A-17F are representative gradient-echo images showing the effectof the FeRh mm-scale disk of FIG. 16 on the surrounding agarose as thetemperature of the set-up is swept through a physiologically relevanttemperature range (10-55° C.) at a constant MM magnetic field of 4.7Tesla;

FIG. 17G is a graph of a width of an image artifact (or MRI signal) ofFIGS. 17A-17F that is created by signal loss due to the magnetic fieldgradients from the FeRh disk of FIG. 16 as a function of the set-uptemperature;

FIG. 18A is a graph of a magnetic moment of a magnetocaloric materialversus temperature, which shows a transition from a first magnetic stateto a second magnetic state, in which the center of the first ordermagnetic phase transition of the magnetocaloric material is at thephysiological temperature of 37° C.;

FIG. 18B is a graph of a magnetic moment of a magnetocaloric materialversus temperature, which shows a transition from a first magnetic stateto a second magnetic state, in which the center of the first ordermagnetic phase transition of the magnetocaloric material is greater thanthe physiological temperature of 37° C.;

FIG. 18C is a graph of a magnetic moment of two magnetocaloric materialsthat have phase transitions at two different magnetic field values atthe physiological temperature;

FIG. 19A is a graph of a magnetic moment of first magneticallymanipulatable material versus temperature, in which the magneticallymanipulatable material is Fe—La—Si;

FIG. 19B is a graph of a magnetic moment of first magneticallymanipulatable material versus temperature, in which the magneticallymanipulatable material is 99% purity FeRh;

FIG. 20 is a flow chart of a procedure performed by the apparatus ofFIG. 2 for using the magnetic apparatus and the magneticallymanipulatable structure to control, alter, or operate on the sample; and

FIG. 21 is a flow chart of a procedure performed by the apparatus ofFIG. 9 for actuating (for example, activating and de-activating) abiological construct (which can be the thermally-sensitive biologicalconstruct within the sample.

DETAILED DESCRIPTION

Referring to FIG. 1, an apparatus 100 is shown that uses a magneticapparatus 105 to perform one or more functions or operations on a sample115. The sample 115 is a three-dimensional body. The sample 115 can be abiological or physiological organism or tissue and can be alive. Themagnetic apparatus 105 includes a magnet 120 that defines a samplevolume 110 that is large enough to accommodate the sample 115. Themagnet 120 is configured to create a magnetic field having a magnitude Bin the sample 115. The apparatus 100 includes an energy supply 125connected to the magnet 120 and a control system 140 connected to one ormore components (such as the energy supply 125 and the magnet 120) ofthe magnetic apparatus 105.

The magnetic apparatus 105 includes a magnetically manipulatablestructure 135 embedded within the body of the sample 115. Themagnetically manipulatable structure 135 is controlled by at least themagnet 120 to affect the function of and operation of the sample 115.The magnetically manipulatable structure 135 includes one or moremagnetically manipulatable materials, which can be magnetocaloricmaterials. The magnetocaloric material is a material that exhibits atransition between a first magnetic state and a second magnetic state inresponse to a change in a property associated with the sample 115 whilethe magnetic field having the magnitude B is maintained in the sample115. This transition can be used to affect the function of or operationof the sample 115. Additionally, the magnetocaloric material experiencesa temperature change in response to a changing magnetic field and thistemperature change can be used to affect the function of or operation ofthe sample 115. The magnetically manipulatable material 135 has magneticproperties that can be changed and this change can occur around thetemperature of a living organism and also in the presence of large DCmagnetic fields of MRI scanners.

While the magnetically manipulatable structure 135 is shown as amonolithic structure in the sample 115 in FIG. 1, it is possible for themagnetically manipulatable structure 135 to be a diffuse or disconnectedstructure 135 within the sample 115. For example, the structure 135 caninclude some materials in one region of the sample 115 and othermaterials in another distinct and separate region of the sample 115.

Magnetocaloric materials can have a sharp and tunable transition ofmagnetization with respect to changes in an environment in which themagnetocaloric material is placed. For example, if the magnetocaloricmaterial is within a sample (such as the sample 115), then themagnetocaloric material has a sharp and tunable transition ofmagnetization with respect to changes in one or more properties of thesample when the sample is held at a particular magnetic field. A sampleproperty that can be changed is the temperature or the magnetic field ofthe sample 115. If the sample 115 is a biological sample, then it isheld at a magnetic field that is suitable for the biological sample, andalso held at temperatures that are suitable, for example, a typicalphysiological (body) temperatures and fields of several Teslas (forexample, 1 to 20 Teslas). Thus, magnetocaloric materials can be made tobe sharply visible or invisible (switchable) in typical magneticresonance imaging (MRI) machines in response to small changes inproperties (for example, temperature or magnetic field) associated withthe sample. This makes magnetocaloric materials suitable as sensorsand/or labels in the sample. Moreover, the location and properties ofthese magnetization transitions can be widely tunable in magnetocaloricmaterials by various materials science techniques of alloying, doping,annealing, for example, thus making the MRI sensor and label designpossibilities wide ranging.

Magnetocaloric materials have magnetic properties that provide a closematch to the requirements for the design of high contrast ratioswitchable and tunable MM labels. More specifically, careful examinationof the magnetocaloric materials' magnetic properties reveals that someof them have extremely sharp first-order magnetic phase transitions attypical physiological temperatures and in the presence of the largeTesla-scale magnetic fields typical of MRI settings. Furthermore, thesesharp first-order magnetic phase transitions can have a positive ornegative slope of magnetization vs. temperature, making them evenstronger candidates as versatile materials for high differentialcontrast switchable MRI labels. Finally, magnetocaloric materials can beengineered and their magnetic properties fine-tuned through materialsscience techniques such as doping, alloying, thermal treatments and thelike to optimize their response under physiological and MM-appropriateconditions. As discussed below, the basic magneto-physical and MMmeasurements on samples of iron-rhodium (FeRh) are described in order todevelop the case for and demonstrate the use of such materials for highdifferential contrast ratio MRI labels.

For example, the magnetocaloric material is a material selected from thegroup consisting of iron-rhodium (FeRh), alloys of iron-rhodium, alloysof manganese arsenide, Heusler alloys, alloys of manganese-iron, alloysof lanthanum, iron, and silicon, and gadolinium.

Accordingly, as discussed herein, magnetocaloric materials can be usedas tunable and switchable labels and sensors for MRI applications. Thesemagnetocaloric materials have sharp magnetic phase transitions attypical physiological temperatures and in the presence of the large DCmagnetic field values associated with MM machines. This means that theyhave a sharp change in magnetization for a small change in temperatureor magnetic field in the experimental settings typical of MM machines,which makes them uniquely suitable as MM contrast agents and sensors. Achange of magnetization of the magnetocaloric material can be detectedin MM by observing the effect this change in magnetization has on wateror biological tissue surrounding the material. Furthermore, the magneticproperties of magnetocaloric materials can be tuned by appropriatematerials science technique of alloying, doping, and temperaturetreatments, for example.

Magnetocaloric materials can be used as sensors of temperature ormagnetic field in typical MRI settings of physiological temperature andlarge bias magnetic fields of 1-20 Tesla. Magnetocaloric materials canbe used as switchable MM labels in typical MM settings of physiologicaltemperature and large bias magnetic fields of 1-20 Tesla.

Magnetocaloric materials can be switched on or off in typical MMsettings of physiological temperature and large bias magnetic fields of1-20 Tesla by either a change in magnetic field or a change intemperature or a combination of both. Magnetocaloric materials can havepositive or negative slope of magnetization vs. temperature, which meansthat the labels can be made to be positive labels (can turn on with risein temperature) or negative labels (can turn off with rise intemperature). This also means that multiple labels can mixed so thatsome turn on and some off with rise and temperature, and vice versa.

Magnetocaloric materials can be engineered and therefore tuned to havetransitions at different magnetic fields and temperatures. This meansthat these materials can be used as labels so that they are visible orinvisible at different magnetic fields of MRI machines.

Referring to FIG. 2, in some implementations, the magneticallymanipulatable structure 135 is a magnetically manipulatable structure235 embedded within a sample 215 that is to be imaged within an imagingapparatus 200. The imaging apparatus 200 includes a magnetic apparatus205 that defines a sample volume 210 that is large enough to accommodatethe sample 215 to be imaged. The magnetically manipulatable structure235 includes and one or more magnetically manipulatable materials 236.The magnetic apparatus 205 includes a magnet 220 that is configured tocreate a magnetic field having a magnitude B in the sample 215. Eachmagnetically manipulatable material 236 is a material that exhibits atransition between a first magnetic state and a second magnetic state inresponse to a change in a property associated with the sample while themagnetic field having the magnitude B is maintained in the sample. Thus,each magnetically manipulatable material 236 can be a magnetocaloricmaterial.

The apparatus 200 includes an energy supply 225 connected to the magnet220. The magnet 220 can be formed from electrically conductive wirecoils through which current from the energy supply 225 is passed. Theenergy supply 225 can provide a direct current (DC) to the wire coils,which means that the energy supply 225 provides a constant voltage orcurrent to the wire coils of the magnet 220. Thus, the energy supply 225can, for example, include an alternating current (AC) generator equippedwith a device to produce the direct current, a device that converts ACto DC, or batteries to provide DC. In some implementations, the magnet220 can be a superconducting magnet.

In some implementations, the magnetic field magnitude B is greater than0.5 Tesla. In other implementations, the magnetic field magnitude B isin a range of 1-20 Tesla. The magnitude B of the magnetic field islimited by the design of the magnet 220. Thus, for example, if themagnet 220 is a superconducting magnet, then the magnitude B can be aslarge as 20 Tesla. The large value of the magnitude B allows forhigher-quality imaging, and the superconductivity enable the imagingapparatus to work more efficiently.

In some implementations, the first magnetic state of the magneticallymanipulatable material 236 is an antiferromagnetic state or aparamagnetic state, which means that the magnetically manipulatablematerial 236 is so weakly magnetic that it is considered to benon-magnetic. In an antiferromagnetic state, adjacent moments thatbehave as tiny magnets spontaneously align themselves into opposite, orantiparallel, arrangements throughout the magnetically manipulatablematerial 236 so that the material 236 exhibits almost no gross externalmagnetism. In antiferromagnetic materials, the magnetism from magneticmoments oriented in one direction is canceled out by the set of magneticmoments that are aligned in the reverse direction. In a paramagneticstate, some of the atoms or ions in the magnetically manipulatablematerial 236 have a net magnetic moment due to unpaired electrons inpartially filled orbitals; however, the individual magnetic moments donot interact magnetically, and the magnetization is zero when a field isremoved. In the presence of a field, there is now a partial alignment ofthe atomic magnetic moments in the direction of the field, resulting ina net positive magnetization and positive susceptibility.

In some implementations, the second magnetic state of the magneticallymanipulatable material 236 is a ferromagnetic state or a ferrimagneticstate, which means that the material is considered to be magnetic. In aferromagnetic state, the spins in the material 236 exhibit parallelalignment of moments resulting in large net magnetization even in theabsence of a magnetic field. In a ferrimagnetic state, the opposingmoments of the spins in the material 236 are unequal and a spontaneousmagnetization remains in the absence of a magnetic field.

If the sample 215 is a living physiological or biological tissue, thenthe magnetically manipulatable material 236 exhibits the transitionwhile the temperature in the sample is at a physiological temperature,for example, between 270 and 370 Kelvin (K).

The property associated with the sample 215 that is altered can be atemperature. The transition occurs in response to a change intemperature that is less than a fraction of the temperature of thesample 215. For example, the change in temperature can be a factor often times smaller than the temperature of the sample 215. Thus, if thetemperature of the sample 215 is about 270-370 K, then the temperaturechange can be about 10-40 K.

The property associated with the sample 215 that is altered can be amagnetic field of the sample. In this case, the transition occurs inresponse to a change in a magnitude of a magnetic field (ΔB), where thechange in magnitude ΔB that is substantially smaller than the magnitudeB of the magnetic field. The change in magnitude is substantiallysmaller than the magnitude B if it is a fraction of the magnitude B, anorder of magnitude smaller than the magnitude B, or at least an order ofmagnitude smaller than the magnitude B.

The imaging apparatus 200 also includes a sample property scanningsystem 245 configured to change the property of the sample 215 while themagnetic field having magnitude B is maintained in the sample 215. Thesample property scanning system 245 therefore acts to cause thetransition in the magnetically manipulatable material 236.

In some implementations, the sample property scanning system 245includes a temperature scanning system for changing, as the property, atemperature of the sample 215. The temperature scanning system includesan apparatus thermally connected to the sample 215. The thermallyconnected apparatus includes an induction heater that operates at eithera medium frequency or a radio frequency range and includes a controller,and a heat inductor. The heat inductor can be a heating coil.

In other implementations, the sample property scanning system 245includes a magnetic scanning system for changing, as the property, amagnetic field of the sample 215. The magnetic scanning system includesa magnetic source that is configured to change the magnetic field of thesample 215.

In some implementations, the magnetic apparatus 205 is a magneticresonance imaging (MRI) apparatus. In this case, imaging apparatus 200can include, in addition to the magnet 220 shown in FIG. 2, one or moregradient magnets 250 configured to produce a variable magnetic fieldthat ranges in strength an amount that is much less than (for example,one hundredth of) the magnitude B. This variable magnetic field canpermit different parts of the sample 215 to be scanned. The imagingapparatus 200 can also include an electromagnetic source 255 configuredto produce a varying electromagnetic field having a range of magneticfield magnitude that is much less than (for example, one hundredth of)the magnitude B. The varying electromagnetic field can be aradiofrequency field and can be produced by a set of coils that transmitthe radiofrequency waves into specific regions of the sample 215.

If the magnetically manipulatable material 236 is not inherently foundin the sample 215, then it can be added to the sample 215. For example,the imaging apparatus 200 can include a delivery (or injection)apparatus 260 configured to transport the magnetically manipulatablematerial 236 from a source 261 of the material into the sample 215. Themagnetically manipulatable material 236 can be in the form of aplurality of spatially-separated particles. The particles are dispersedthroughout at least one region of interest within the sample. If thesample 215 is a living organism, then the size of the particles can beon the order of the size of cells within the sample 215. For example,the size of the particles is on the order of micrometers, for example,1-10 micrometers (μm). In some implementations, each particle has amicroscopic size (which means it is only viewable with the use of amicroscope).

The particles of the magnetically manipulatable material 236 can beprepared prior to delivery into the sample 215 to be in a suitable statefor operation or use in the sample 215.

If the sample 215 is a living organism, the sample 215 is held at aphysiological temperature to maintain the organism in a living state.

The imaging apparatus 200 includes a detector 270 that detects a signalproduced as a result of the interaction between the magnetic field andthe sample 215. The imaging apparatus 200 can also include some sort ofoutput device 275 such as a display. Additionally, the imaging apparatusincludes a control system 240 connected to the magnetic apparatus 205.The control system 240 is also connected to the other components of theimaging apparatus 200 such as the property scanning system 245, theelectromagnetic source 255, the gradient magnets 250, the injectionapparatus 260, the detector 270, the display 275, and the energy supply225. The control system 240 is configured to: receive data output fromthe detector 270, the output relating to the detected signal; analyzethe received data; and estimate the sample property based on theanalysis. The control system 240 is also configured to create an imageof the sample 215 at the display 275 based on the analysis.

The detector 270 detects the signal produced as a result of theinteraction between the magnetic field and the sample 215 by detecting asignal produced by tissue within the sample 215 that is in proximity tothe magnetically manipulatable material 236. The signal produced bytissue within the sample 215 that is in proximity to the magneticallymanipulatable material 236 includes electromagnetic radiation generatedfrom protons within the sample 215 in proximity to the magneticallymanipulatable material 236.

The magnetically manipulatable material 236 remains magneticallyunsaturated while the magnetic field having the magnitude B exists inthe sample 215. This means that the magnetically manipulatable material236 is capable of exhibiting a transition between the first magneticstate and the second magnetic state even while the magnetic field havingthe magnitude B exists in the sample 215.

In some implementations, the magnetically manipulatable structure 235includes one or more different magnetically manipulatable materials 236or magnetocaloric materials. In these implementations, each differentmagnetically manipulatable material 236 in the structure can have atransition that occurs in response to a distinct change in the propertyof the sample 215. For example, a first magnetically manipulatablematerial 236 has a transition from the first magnetic state to thesecond magnetic state that occurs in response to an increase in thesample property; and a second magnetically manipulatable material 236has a transition from the first magnetic state to the second magneticstate that occurs in response to a decrease in the sample property. Asanother example, a first magnetically manipulatable material 236 has atransition from the first magnetic state to the second magnetic statethat occurs in response to an increase in the sample property; and asecond magnetically manipulatable material 236 has a transition from thesecond magnetic state to the first magnetic state that occurs inresponse to an increase in the sample property. As a still furtherexample, a first magnetically manipulatable material 236 has atransition between the first magnetic state and the second magneticstate that occurs in response to a change in a first sample property;and a second magnetically manipulatable material 236 has a transitionbetween the first magnetic state and the second magnetic state thatoccurs in response to a change in a second sample property that isdistinct from the first sample property.

In other implementations, the transition from the first magnetic stateto the second magnetic state occurs in a first range of values of theproperty as the property is increased; the transition from the secondmagnetic state to the first magnetic state occurs in a second range ofvalues of the property as the property is decreased; and the first rangeof values is distinct from the second range of values.

FIG. 3A shows a magnetic state M (or magnetic moment) of themagnetically manipulatable material 236 versus the sample property,where the sample property is the temperature T of the sample 215. In theimplementation shown in FIG. 3A, the magnetically manipulatable material236 transitions from a first magnetic state 300 to a second magneticstate 305 at a transition temperature T(tr). In this implementation, thefirst magnetic state 300 is magnetic, for example, ferromagnetic orferrimagnetic, and the second magnetic state 305 is non-magnetic, forexample, an antiferromagnetic or a paramagnetic. Moreover, thistransition occurs while the magnetic field having the magnitude B ismaintained in the sample 215, where the magnitude B is a value between1-10 T. The transition temperature T(tr) can be between 270 K and 370 Kor around 310 K.

FIG. 3B shows a magnetic state M (or magnetic moment) of themagnetically manipulatable material 236 versus the sample property,where the sample property is the temperature T of the sample 215. In theimplementation shown in FIG. 3B, the magnetically manipulatable material236 transitions from a first magnetic state 310 to a second magneticstate 315 at a transition temperature T(tr). In this implementation, thefirst magnetic state 310 is non-magnetic, for example, antiferromagneticor paramagnetic, and the second magnetic state 315 is magnetic, forexample, ferromagnetic or ferrimagnetic. Moreover, this transitionoccurs while the magnetic field having the magnitude B is maintained inthe sample 215, where the magnitude B is a value between 1-10 T. Thetransition temperature T(tr) can be between 270 K and 370 K or around310 K.

FIG. 4 shows a magnetic state M (or magnetic moment) of the magneticallymanipulatable material 236 versus the sample property, where the sampleproperty is the magnetic field (represented by the magnitude B) withinthe sample 215. In the implementation shown in FIG. 4, the magneticallymanipulatable material 236 transitions from a first magnetic state 400to a second magnetic state 405 at a first transition magnetic fieldmagnitude B1(tr), and from the second magnetic state 405 to a thirdmagnetic state 410 at a second transition magnetic field magnitude B2(tr). In this implementation, the first magnetic state 400 isnon-magnetic, for example, antiferromagnetic or paramagnetic; the secondmagnetic state 405 is also non-magnetic, and the third magnetic state410 is magnetic. Moreover, these transitions occur while the temperaturewithin the sample 215 is maintained at a temperature T, which can have avalue between 270 K and 370K or around 310K. The magnitude B1(tr) can beany value between 1-10 T, for example 4 T, and the magnitude B2(tr) canbe any other value between 1-10 T, for example, 5 T.

FIG. 5A shows a magnetic state M (or magnetic moment) of themagnetically manipulatable material 236 versus the sample property,where the sample property is the magnetic field (represented by themagnitude B) within the sample 215, while maintaining the sample 215 ata constant temperature T. The transition from the first magnetic state500 to the second magnetic state 505 occurs at a magnitude B1(tr) whilethe magnitude B is increased. On the other hand, the transition from thesecond magnetic state 505 to the first magnetic state 500 occurs at adifferent magnitude B2(tr) while the magnitude is decreased. Themagnitude B2(tr) is less than the magnitude B1(tr). This is because ofthe hysteresis effect (in which the physical effect, that is, themagnetic state M, on the sample 215 is retarded or changed depending howthe sample property is changed).

FIG. 5B shows a magnetic state M (or magnetic moment) of themagnetically manipulatable material 236 versus the sample property,where the sample property is the temperature (represented by T) withinthe sample 215, while maintaining the sample 215 at a constant magneticfield magnitude B. The transition from the first magnetic state 510 tothe second magnetic state 515 occurs at a temperature T1(tr) while thetemperature T is increased. On the other hand, the transition from thesecond magnetic state 515 to the first magnetic state 510 occurs at adifferent temperature T2(tr) (which is less than the temperature T1(tr))while the temperature T is decreased because of the hysteresis effect.

Furthermore, it is possible that the magnetically manipulatable material236 only exhibits a transition in response to a change in two sampleproperties.

As mentioned above, and referring to FIG. 6A, the magneticallymanipulatable structure 235 can include a plurality of differentmagnetically manipulatable materials 236 (that is, two or moremagnetically manipulatable materials) within the sample 215. In thisexample, there are two magnetically manipulatable materials 236 a and236 b contained or embedded within the sample 215. FIG. 6B shows anexample of a graph of a magnetic state M (or magnetic moment) of the twomagnetically manipulatable materials 236 a, 236 b within the sample 215versus the sample property, where the sample property is the magneticfield (represented by the magnitude B) within the sample, whilemaintaining the sample 215 at a constant temperature T. In thisimplementation, the two magnetically manipulatable materials 236 a, 236b have different transition points in response to a change in themagnetic field magnitude B.

The behavior of the first magnetically manipulatable material 236 a isshown in the red graph 602 and the behavior of the second magneticallymanipulatable material 236 b is shown in the green graph 612. The firstmagnetically manipulatable material 236 a transitions from its firstmagnetic state 600 to its second magnetic state 605 at a magnetic fieldmagnitude B1(tr) as the magnetic field magnitude B is being increasedwhile the first magnetically manipulatable material 236 a transitionsfrom its second magnetic state 605 to its first magnetic state 600 at amagnetic field magnitude B2(tr) as the magnetic field magnitude B isbeing decreased. The second magnetically manipulatable material 236 btransitions from its first magnetic state 610 to its second magneticstate 615 at a magnetic field magnitude B3(tr) as the magnetic fieldmagnitude B is being increased while the second magneticallymanipulatable material 236 b transitions from its second magnetic state615 to its first magnetic state 610 at a magnetic field magnitude B4(tr)as the magnetic field magnitude B is being decreased. These transitionspoints B1(tr), B2(tr), B3(tr), and B4(tr) are distinct from each other.For example, if the magnetic field magnitude B generally remains between1-10 T and the temperature at which the sample 215 is held is about 310K, then the transition point B1(tr) can be 4.4 T, the transition pointB2(tr) can be 3.7 T, the transition point B3(tr) can be 6.7 T, and thetransition point B4(tr) can be 5.7 T. In this example, both of themagnetically manipulatable materials 236 a, 236 b are non-magnetic below3.7 T, both of the magnetically manipulatable materials 236 a, 236 b aremagnetic above 6.7 T, and the first magnetically manipulatable material236 a is magnetic while the second manipulatable material 236 b isnon-magnetic at 4.7 T.

In some implementations, the magnetically manipulatable material 236transitions from a magnetic to a non-magnetic state with a rise in thesample property. For example, as shown in FIG. 7A, a first magneticallymanipulatable material transitions from a magnetic state 700 to anon-magnetic state 705 at the transition temperature T1(tr) as thesample property of temperature T is increased while the firstmagnetically manipulatable material transitions from the non-magneticstate 705 to the magnetic state 700 at the transition temperature T2(tr)as the sample property of temperature T is decreased. In this example,the magnetic field magnitude B is held constant. As an example, thematerial Iron—Lanthanum—Silicon (Fe—La—Si) behaves in this manner.

In other implementations, the magnetically manipulatable material 236transitions from a non-magnetic to a magnetic state with a rise in thesample property. For example, as shown in FIG. 7B, a second magneticallymanipulatable material transitions from a non-magnetic state 710 to amagnetic state 715 at the transition temperature T3(tr) as the sampleproperty of temperature T is increased while the second magneticallymanipulatable material transitions from the magnetic state 715 to thenon-magnetic state 710 at the transition temperature T4(tr) as thesample property of temperature T is decreased. In this example, themagnetic field magnitude B is held constant. For example, the materialFeRh behaves in this manner.

If both the first and the second magnetically manipulatable materials ofFIGS. 7A and 7B are within the sample 215, such as shown in FIG. 6A,then an exemplary combined transition graph is shown in FIG. 8 in whichthe transition temperature T3(tr) is equal to the transition temperatureT1(tr) and the transition temperature T4(tr) is equal to the transitiontemperature T2(tr). In this implementation, the first and secondmagnetically manipulatable materials 236 a, 236 b can be switched on anoff (that is, transitioned from the magnetic state to the non-magneticstate) in opposite manners. For example, the second magneticallymanipulatable material 236 b is magnetic and the first magneticallymanipulatable material 236 a is non-magnetic above the transitiontemperature T3(tr) (and T1(tr)) while the first magneticallymanipulatable material 236 a is magnetic and the second magneticallymanipulatable material 236 b is non-magnetic below the transitiontemperature T4(tr) (and T4(tr)). In this example, the temperature can beadjusted in a range of 250 K to 350 K.

While only two magnetically manipulatable materials 236 a and 236 b arediscussed above, it is possible for the magnetically manipulatablestructure 235 to include more than two different types of thesematerials.

Referring to FIG. 9, in other implementations, the magneticallymanipulatable structure 135 is a magnetically manipulatable structure935 embedded within a sample 915 of an apparatus 900. The apparatus 900is designed to use magnetocaloric materials as physical actuators ofbiological constructs in genetically-modified cells while in a DCmagnetic field. For simplicity, components shown in FIG. 9 are merely inblock diagram form and are not to scale. A change to a property of themagnetocaloric material causes a change in the status of the biologicalconstruct because the magnetocaloric material is physically coupled withthe biological construct. A physical coupling means that there is acoupling that is based on an exchange of matter or energy. For example,the physical coupling could be a thermal coupling. As another example,the physical coupling could be an electromagnetic coupling. The propertyof the magnetocaloric material that can be changed can be its magneticstate. The property of the magnetocaloric material that can be changedcan be its temperature.

In some implementations, and as described herein, the property of themagnetocaloric material that is changed is the temperature, and thetemperature of the magnetocaloric material is changed by a change inmagnitude B of the magnetic field applied to the sample 915. In theseimplementations, the physical coupling between the magnetocaloricmaterial and the biological construct is a thermal coupling and thebiological construct is a thermally-sensitive biological construct.

The apparatus 900 includes a magnetic apparatus 905 that defines anactuation volume 910 that is large enough to accommodate the sample 915.The magnetic apparatus 905 includes a magnet 920 that is configured tocreate a magnetic field having a magnitude B in the sample 915 whensupplied with a DC current from a DC energy supply 925.

The apparatus 900 includes at least one thermally-sensitive biologicalconstruct 930 within the sample 915. The magnetically manipulatablestructure 935 is a magnetocaloric actuator 935 thermally coupled withthe thermally-sensitive biological construct 930. While one construct930 and one actuator 935 is shown, it is possible to have a plurality ofconstructs 930 or a plurality of actuators 935 associated with eachconstruct. Thermal coupling between two elements means that the heat isfreely conducted between those two elements. Thus, heat is able to bethermally conducted between the biological construct 930 and theactuator 935. Thermal coupling between two elements can mean that thetwo elements are near enough to each other so that heat does notdissipate substantially into the sample 915 before being conductedbetween the two elements. Thermal coupling between two elements can meanthat the two elements have relative sizes that are complementary so thatheat transfer between the two elements is enabled.

A change in the magnitude B of the magnetic field supplied with the DCcurrent from the supply 925 to the magnet 920 causes the temperature ofthe magnetocaloric actuator 935 to change, and this change causes achange in a status of the thermally-sensitive biological construct 930.

The apparatus 900 therefore operates under the application of a DCmagnetic field, or a magnetic field that is very close to DC. That is,the magnetic field changes relatively slowly at the location of theactuator 935.

The apparatus 900 also includes a control system 940 connected to the DCenergy supply 925 to control the operation of the DC energy supply 925.

The magnetocaloric actuator 935 can include one or more magneticallymanipulatable materials 936 i. The magnetically manipulatable material936 i exhibits a transition between a first magnetic state and a secondmagnetic state in response to the change in the magnitude B of themagnetic field produced by the magnet 920. For example, the magneticallymanipulatable material 936 i of the actuator 935 exhibits the transitionwhile the temperature in the sample 915 is between 270 and 370 K. Themagnetically manipulatable material 936 i of the actuator 935 caninclude a material selected from the group consisting of iron-rhodium(FeRh), alloys of iron-rhodium, alloys of manganese arsenide, Heusleralloys, alloys of manganese-iron, alloys of lanthanum, iron, andsilicon, and gadolinium.

Each magnetically manipulatable material 936 i is a spatially-separatedparticle having a size that is large enough to retain heat long enoughto cause the change in status in the thermally-sensitive biologicalconstruct 930. For example, a cell in a living organism can be between1-50 μm in diameter. If the biological construct 930 is on the order ofa nanometer (nm), then the magnetocaloric actuator 935 can have a sizeon the order of about 1-100 μm.

The sample 915 can be a region of a live human body. In thisimplementation, the magnetically manipulatable material 936 i of theactuator 935 exhibits the transition while the temperature in the livehuman body region is at a human body temperature. In someimplementations, the sample 915 is a living organism and the sample 915is held at a physiological temperature to maintain the organism in aliving state.

The transition between the first magnetic state and the second magneticstate of the magnetically manipulatable material 936 i can occur inresponse to a change in a magnitude of a magnetic field that issubstantially smaller than the overall magnitude B of the magnetic fieldproduced by the magnet 920.

The temperature change caused to the magnetocaloric actuator 935 occurswithout causing a change in status of materials within the sample 915other than the at least one thermally-sensitive biological construct930. In this way, the apparatus 900 is able to finely heat and cool inlocal areas of the sample 915 without causing large-scale heating orcooling to other areas of the sample 915.

In some implementations, the magnet 920 includes electrically conductivewire coils through which current from the DC energy supply 925 ispassed. Thus, the DC energy supply 925 provides the DC current suppliedto the wire coils. In some implementations, the magnet 920 is asuperconducting magnet. And, the magnetic apparatus 905 can be amagnetic resonance imaging apparatus.

Moreover, the magnetic field magnitude B is greater than 0.5 Tesla or ina range of 1-20 Tesla. The magnitude B of the magnetic field can be in arange that does not cause any detrimental changes to the sample 915.That is, the sample 915 does not deteriorate or degrade due to themagnitude B of the magnetic field that is created.

The temperature change dT that occurs in the magnetocaloric actuator 935is governed by the following equation.

${{dT} = {{- \frac{T}{C_{B}}} \times \left( \frac{\partial M}{\partial T} \right)_{B}{dB}}},$

where T is the temperature of the magnetocaloric actuator 935, C_(B) isthe heat capacity of the magnetocaloric actuator 935, ∂M/∂T is the slopeof the magnetization M of the magnetocaloric actuator 935 versus thetemperature T at the specific magnetic field B, and dB is the change inmagnetic field applied to the magnetocaloric actuator 935 by the magnet920. The temperature T of the actuator 935 changes as the magnetic fieldmagnitude B changes. Moreover, the slope ∂M/∂T is an inherent propertyof the magnetocaloric actuator 935. As an example, the magnetocaloricactuator temperature change dT is at least 5° C. for a change inmagnitude of the magnetic field dB between 1-20 T.

In another example, if the magnetic field B supplied by the magnet 920changes from 0 T to 2 T, then the value of dB is 2 T. As anotherexample, if the magnetic field B supplied by the magnet 920 changes from3 T to 5 T, then the value of dB is 2 T. The magnetically manipulatablematerials 936 i that are selected for the magneto-caloric actuator 935are selected to provide a temperature change dT for as small a change inmagnetic field B. Thus, the value of ∂M/∂T for the magneticallymanipulatable materials 936 i is as large as possible or at a maximum attypical physiological (biological) temperatures T (for example, around37° C.). In particular, materials 936 i that have suitable values of∂M/∂T include gadolinium and FeRh. Other materials can have a largevalue of ∂M/∂T at temperatures T that are not typical physiological orbiological temperatures, and those other materials would not be suitablefor use in a physiological or biological sample 915.

If the magnetic apparatus 205 is an MRI machine, then the apparatus 900can include one or more of the other components for operating the MRImachine. For example, the apparatus 900 can also include one or more ofthe property scanning system 245 (which is used to scan or change themagnetic field of the sample 915 in this implementation), theelectromagnetic source 255, the gradient magnets 250, the detector 270,and the display 275.

FIGS. 10A and 10B are block diagrams of an implementation in which theat least one thermally-sensitive biological construct 930 within thesample 915 is an ion channel 1030 positioned along a cellular structure1017 (for example, a cell membrane) of the sample 915. The at least onemagnetocaloric actuator 1035 is a magnetocaloric actuator 1035 thatincludes a plurality of magnetically manipulatable materials 936 i nearthe ion channel 1030. The ion channel 1030 has a status that is eitherclosed (FIG. 10A) or open (FIG. 10B). For example, when closed, the ionchannel 1030 blocks other elements (such as molecules, ions, or atoms)nearby and within the sample 915 from passing through the cellularstructure 1017. When open, the ion channel 1030 permits these othernearby elements (such as molecules, ions, or atoms) to freely passthrough the cellular structure 1017 as long as the opening is largeenough to accommodate the size of the element.

Temperature sensitive ion channels 1030 can be integrated into the cellmembrane (the cellular structure 1017) using a suitable technique suchas cloning or genetic engineering. For example, the ion channel 1030 canbe genetically engineered into the cellular structure 1017. This meansthat the ion channel 1030 may not be present in the wild-type ornon-engineered cellular structure 1017 of the sample 915. The cellularstructure 1017 can be genetically altered through the exogenous deliveryof a portion of deoxyribonucleic acid (DNA) comprising a gene thatexpresses the ion channel 1030 in the sample 915. For example,transgenic expression of a temperature-activated ion channel in a cellcomprising the sample 915 leads to the insertion of the ion channel 1030into the cell membrane, identified as the cellular structure 1017.

In some implementations, the ion channel 1030 is a transient receptorpotential cation channel subfamily V member (such as TRPV1 or TRPV4).The TRPV channel changes its state from closed to open by warming up byabout 5-10° C. Thus, the change in magnitude B of the magnetic fieldsupplied to the sample 915 should be large enough to increase thetemperature of the magnetocaloric actuator 1035 by enough of an amountsuch that the temperature of the TRPV increases by about 5° C.

As another example, the ion channel 1030 is a transient receptorpotential cation channel subfamily M member (such as TRPM8). Bycontrast, the TRPM channel changes its state from closed to open bycooling down by about 5-10° C. Thus, the change in magnitude B of themagnetic field supplied to the sample 915 should be large enough todecrease the temperature of the magnetocaloric actuator 1035 by enoughof an amount so that the temperature of the TRPM decreases by about 5°C.

Referring also to FIG. 9, in some implementations, an increase in themagnitude B of the magnetic field supplied with the DC energy supply 925causes an increase in the temperature of the magnetocaloric actuator 935and an increase in the temperature of the thermally-sensitive biologicalconstruct 930. And, a decrease in the magnitude B of the magnetic fieldsupplied with the DC energy supply 925 causes a decrease in thetemperature of the magnetocaloric actuator 935 and a decrease in thetemperature of the thermally-sensitive biological construct 930. Forexample, a magnetocaloric actuator 1035 in which its magneticallymanipulatable material 936 i includes gadolinium exhibits this property.For example, the temperature of gadolinium (as the magneticallymanipulatable material 936 i) increases by about 2.5-3.0° C. for every 1T increase in the magnitude B of the magnetic field at a physiologicalor biological temperature.

In other implementations, an increase in the magnitude B of the magneticfield supplied with the DC energy supply 925 causes a decrease in thetemperature of the magnetocaloric actuator 935 and a decrease in thetemperature of the thermally-sensitive biological construct 930.Moreover, a decrease in the magnitude B of the magnetic field suppliedwith the DC energy supply 925 causes an increase in the temperature ofthe magnetocaloric actuator 935 and an increase in the temperature ofthe thermally-sensitive biological construct 930. A magnetocaloricactuator 935 in which its magnetically manipulatable material 936 iincludes an alloy of iron-rhodium (FeRh) exhibits this property. Forexample, the temperature of FeRh (as the magnetically manipulatablematerial 936 i) decreases by about 6.5° C. for every 1 T increase in themagnitude B of the magnetic field at a physiological or biologicaltemperature.

Thus, in this way, the apparatus 900 can be used to either heat or coolthe actuator 935, and because of this flexibility, there are moreoptions for how to affect the thermally-sensitive biological construct930.

FIG. 11 is a block diagram of a sample 1115 that includes a plurality ofthermally-sensitive biological constructs 1130A, 1130B, . . . 1130K(where K is an integer greater than 2). In some implementations, thesebiological constructs 1130A, 1130B, . . . 1130K can be associated withthe same structure within the sample 1115. In other implementations, oneor more of these biological constructs 1130A, 1130B, . . . 1130K areassociated with a structure that is different from the structuresassociated with the other biological constructs. Moreover, amagnetocaloric actuator 1135 can be associated with each of thesebiological constructs. For example, a magnetocaloric actuator 1135 i isthermally coupled with a first thermally-sensitive biological construct1130A, a magnetocaloric actuator 1135 j is thermally coupled with asecond thermally-sensitive biological construct 1130B, . . . and amagnetocaloric actuator 1135 k is thermally coupled with a lastthermally-sensitive biological constructs 1130K. Each magnetocaloricactuator 1135 i, 1135 j, . . . 1135 k is distinct from each of the othermagnetocaloric actuators.

FIG. 12 is a block diagram of a single magnetocaloric actuator 1235having different magnetically manipulatable materials 1236 i, 1236 j,1236 k that are mixed together (but do not interact with each other).The labels i, j, and k denote three different types of materials. Whileonly three are shown there can be any number of different materials inthe magnetocaloric actuator 1235. For example, the material 1236 i canheat up as the magnetic field is decreased while the material 1236 j cancool down as the magnetic field is decreased.

Referring again to FIG. 9, the apparatus 900 works with a change inmagnetic field that is caused by a DC current from the DC energy supply925, and thus a thermal magnetic treatment in a biological or medicalsample 915 is enabled without the use of AC or RF (radio frequency)fields, which can cause more damage to the sample 915. In Tesla-scalemagnetic fields (such as those used in modern magnetic resonance imagingor NMR spectrometers), temperature differences obtained by themagnetocaloric actuator 935 can be on the order of 10° C. or more.Furthermore, in the implementations of FIGS. 10A and 10B, in which thethermally-sensitive biological construct 1030 is an ion channel 1030positioned along a cellular structure 1017 of the sample 915, these ionchannels 1030 can be inserted into biological cells such as neurons,that are sensitive to heat and cold. Temperature differences on theorder of 5-10° C. are large enough to open or close such ion channels1030. Therefore, magnetically manipulatable materials 936 i can be onthe order of a micron in size (for example 10 μm in diameter), andplaced next to such cells, which can be activated by exposing them tomagnetic fields that change due to changes supplied by a DC energysupply 925. In this way, the ion channel 1030 can be remotely activated,which means that an invasive procedure that disrupts the sample 915 isnot needed in order to activate the ion channel 1030.

Referring to FIG. 13, a test apparatus 1300 is shown for demonstratingthe feasibility of using magnetocaloric materials as thermal actuatorsof temperature-sensitive biological constructs in genetically-modifiedcells while in a DC magnetic field. FIG. 13 shows a schematicrepresentation of the test apparatus 1300 in which the at least onethermally-sensitive biological construct 930 within the sample 915 is anion channel (such as discussed above) 1330 positioned in a cellularstructure 1317 of a neuron 1318 within a biological sample 1315. Thebehavior of the neurons 1318 in the sample 1315 is tested withconductors 1319, through which current flows to a current measurementdevice 1336, and the current value is an indicator of whether theneurons fire in response to some stimulus.

In this test, some of the neurons 1318B are configured with ion channels1330 while some of the neurons 1318A lack any ion channels 1330.Moreover, some of the neurons 1318A that lack ion channels are thermallycoupled with at least one magnetocaloric actuator 1335 while the othersof the neurons 1318A that lack ion channels are not thermally coupledwith a magnetocaloric actuator 1335. Similarly, some of the neurons1318B with the ion channels 1330 are thermally coupled with at least onemagnetocaloric actuator 1335 while the others of the neurons 1318B withthe ion channels 1330 are not thermally coupled with a magnetocaloricactuator 1335. The test apparatus 1300 includes at least one conductor1319 associated with each neuron 1318. Thus, the conductor 1319registers a change in current when the neuron 1318 fires. Moreover, thetest apparatus 1300 can be configured so that a neuron 1318B only fireswhen it is activated by the opening or closing of its ion channel 1330.In this way, the effect of the ion channel 1330 changing its state(between open and close) can be measured or detected with the currentsignal measured from the conductor 1319.

To test, the sample 1315 is placed in an actuation volume (such asvolume 910) and a magnetic field having a magnitude B is applied by themagnet (such as magnet 920). The magnitude B of the magnetic field ischanged (for example, by changing the DC current from the DC energysupply 925). The change of the magnitude B of the magnetic field causesthe temperature of the magnetocaloric actuator 1335 to change, and thistemperature change causes a change in status of the ion channel 1330that is thermally coupled to a magnetocaloric actuator 1335, and thischange in status of the ion channel 1330 causes the neuron 1318B towhich it is associated or in proximity of to fire (or change its currentoutput). Thus, it is expected that the change in magnitude B of themagnetic field leads to only a change in current output of the neurons1318B that are associated with ion channels 1330 that are in thermalcoupling with an actuator 1335, while the neurons 1318B having ionchannels 1330 that are not in thermal coupling with an actuator 1335 andthe neurons 1318A should not produce any change in current output.

Switchable and tunable labels with high contrast ratio are developed forMM using magnetocaloric materials that have sharp first order magneticphase transitions at physiological temperatures and typical MRI magneticfields. Selection of appropriate magnetic materials for tunable labelsin typical MRI settings of Tesla-scale DC magnetic fields andphysiological temperatures of around 37° C. is hampered by the basicphysical properties of most classical magnetic materials such as iron,iron oxides, and the like. Most magnetic materials have Curietemperatures in the hundreds of degrees Celsius, and therefore have avery flat saturation magnetization with respect to temperature at thephysiological body temperatures of around 37° C. (310K). Moreover,standard MRI settings place these labels in large DC magnetic fieldstypically between 1-20 Tesla where all of these materials aremagnetically saturated and therefore have constant contrast in the MRI.Therefore, magnetic materials are identified, designed, or engineeredthat have switchable and tunable properties with high differentialcontrast ratios in the MRI settings where the DC magnetic fields arevery large (on the scale of Teslas) and in-vivo physiologicaltemperatures are around 37° C.

A magnetocaloric material such as iron-rhodium (FeRh) can be prepared bymelt mixing, high-temperature annealing, and ice-water quenching.Temperature and magnetic field dependent magnetization measurements ofwire-cut FeRh samples can be performed on a vibrating samplemagnetometer. Temperature-dependent MRI of FeRh samples can be performedon 4.7T scanner.

The magnetocaloric material FeRh can be demonstrated to act as a highcontrast ratio switchable MM contrast agent due to its sharp first ordermagnetic phase transition in DC magnetic field of MRI and at thephysiologically relevant temperature. A wide range of magnetocaloricmaterials are available that can be tuned by materials sciencetechniques to optimize their response under MRI-appropriate conditionsand be controllably switched in-situ with temperature, magnetic field,or a combination of both.

Examples of the apparatus, materials, and tests performed on thesemagnetically manipulatable materials 236 or 936 i using the apparatusare described next.

Moreover, the development of novel contrast mechanisms and labelingagents for MRI facilitates further the advancements in non-invasive cellimaging, tracking, and readout of physiological conditions in-vivo. Morespecifically, the extremely sharp first-order magnetic phase transitionsthese magnetocaloric materials have at typical physiologicaltemperatures and in the presence of the large DC magnetic field valuesassociated with MM machines provide an ideal match to the requirementsfor the design of novel MRI labels. Furthermore, a wide range ofmagnetocaloric materials are available that can be engineered andfine-tuned to optimize their response under MRI-appropriate conditions.

One magnetocaloric material that can be used is iron-rhodium, which isdiscussed next. The iron-rhodium is prepared by mixing the components(Fe and Rh) in an arc melting furnace. Next, the mixed components aresubjected to a high-temperature annealing in an Argon gas quartz tubefurnace at 1,000° C. for two weeks, and subsequently rapidly quenched inice-water. This procedure typically results in the ordered(body-centered-cubic CsCl-type crystal structure) binary alloy FeRh withthe bulk saturation magnetization of Ms=1.3×10⁶ A/m in the ferromagneticstate. The prepared FeRh can be cut into mm-scale sample disks andbuffed to a shiny metallic surface with an optical fiber polishing paperin order to remove any oxide from the samples. Temperature and fielddependent magnetic measurements of the samples can be performed in a9-Tesla Vibrating Sample Magnetometer (for example, procured from VSM,Quantum Design, Inc.). In order to demonstrate the basicproof-of-concept feasibility of a magnetocaloric material as a tunableand switchable high differential contrast agent at physiologicaltemperatures and typical MM settings, a 4.7 Tesla MM scanner (producedby Bruker Biospin, Inc.) can be used. The available MRI polarizingmagnetic field of such a scanner is closest to the value where the sharpfirst order magnetic phase transition happens near the physiologicaltemperature of 37° C. (310° K).

Two sets of iron-rhodium granules are prepared for testing. The firstset is Fe 49%-Rh 51% atomic composition, of 99% nominal purity and isdiscussed with reference to FIGS. 14A and 15A and the second set is Fe49%-Rh 51% atomic composition, of 99.9% nominal purity) and is discussedwith reference to FIGS. 14B and 15B. The granules of FeRh can beobtained from American Elements Corporation (Model FE-RH-02 for 99%purity or Model FE-RH-03 for 99.9% purity).

In FIGS. 14A-15B, the magnetocaloric material (236 or 936 i) used in themagnetically manipulatable structure is FeRh. FIGS. 14A and 14B show themeasurements of the magnetic moment of the FeRh structure as a functionof temperature at different constant magnetic fields. Measurements aretaken with the 9T vibrating sample magnetometer. Both FeRh structuresexhibited a sharp first order magnetic transition from anantiferromagnetic to a ferromagnetic state over a very narrow range ofphysiologically relevant temperatures, as discussed next.

FIG. 14A shows the measurement of the magnetic moment of a 99% purityFeRh structure as a function of temperature in different bias DCmagnetic fields, for example, 1T (1401A), 3T (1403A), and 5T (1405A).The FeRh structure exhibits a sharp magnetic phase transition from anantiferromagnetic to a ferromagnetic state over a very narrow range ofphysiologically relevant temperatures. More specifically, the FeRhstructure has a sharp transition around body temperature (37° C.=310K)in a constant magnetic field (the DC bias field) of around 1 Tesla.

FIG. 14B shows the measurement of the magnetic moment of a 99.9% purityFeRh structure as a function of temperature in different bias DCmagnetic fields, for example, 1T (1401B), 3T (1403B), 5T (1405B), and 7T(1407B). The FeRh structure exhibits a sharp transition from anantiferromagnetic to a ferromagnetic state over a very narrow range ofphysiologically relevant temperatures. More specifically, the FeRhstructure has a sharp magnetic phase transition around body temperature(37° C.=310K) in the DC bias field of around 5 Tesla.

These results are in line with the previously reported measurements ofFeRh and demonstrate several features. The most important one is thatthe magnetization of FeRh changes through the transition by a factor ofabout 20 in absolute value, and it does so over a very narrowtemperature range around the physiological body temperature and in thepresence of a large Tesla-scale magnetic field. The second feature isthat the temperature dependence and magnetic properties of FeRh (andmagneto-caloric materials in general) are highly dependent on the purityof the FeRh. Conversely, this demonstrates the attractive feature ofFeRh (and other magneto-caloric materials) that, through carefulmaterials science preparation and process control of impurities andcrystal structure, one can tune and engineer FeRh to have a sharpmagnetic phase transition at the desired temperature and bias magneticfield (nominally at the physiological body temperature and magneticfield of the MRI machine used). Furthermore, such temperature dependenceof magnetization demonstrates that, once the proper magneto-caloricmaterial is prepared for a specific magnetic field of the MRI used, themagnetization of that magneto-caloric label can in principle be switchedin-situ by modest temperature changes on the order of a few degreesCelsius.

FIGS. 15A and 15B show the measurements of the magnetic moment of theFeRh structure as a function of varying magnetic field at constanttemperature (at a room temperature of 27° C.=300K or at a physiologicalbody temperature of 37° C.=310K, respectively). Measurements are takenwith the 9T vibrating sample magnetometer.

Referring to FIG. 15A, the magnetization of the FeRh structure is tunedwith the magnetic field. In this measurement, the magnetic moment of a99% purity FeRh structure is measured as a function of the magneticfield at various constant temperatures, for example, 310K (1510A) and300K (1500A). As evident, the sharp transition is present at large DCmagnetic field values and around physiologically relevant temperatures.

Referring to FIG. 15B, the magnetization of the FeRh structure is tunedwith the magnetic field. In this measurement, the magnetic moment of a99.9% purity FeRh structure is measured as a function of the magneticfield at various constant temperatures, for example, 330K (1530B), 320K(1520B), 310K (1510B), and 300K (1500B). Again, the sharp transition ispresent at large DC magnetic field values and around physiologicallyrelevant temperatures.

Specifically, the 99% purity FeRh structure (FIG. 14A) has a sharpmagnetic phase transition around the room and body temperatures at themagnetic field values between 0.5-2 Tesla, while the 99.9% purity FeRhstructure (FIG. 14B) has a sharp magnetic phase transition around theroom and body temperatures at the magnetic field values between 4-6Tesla. These results demonstrate another feature that, once the propermagnetocaloric material is fabricated as a switchable MRI label for thespecific magnetic field of the MM used, the magnetization of thatmagnetocaloric label can be switched in-situ with additionally added orsubtracted magnetic field or by temporarily removing the sample from theMM bore.

Measurements described in FIGS. 14A, 14B, 15A, and 15B guideexperimental choices for demonstrating the basic proof-of-conceptfeasibility of a magnetocaloric FeRh material as a switchable highdifferential contrast MM agent. Of the two FeRh structures that wereprepared, 99.9% purity FeRh structure displayed a sharper first ordermagnetic transition at a higher bias DC magnetic field (of around 5Tesla) at the physiological temperature of 37° C. Referring to FIG. 16,for the MRI demonstration, a testing apparatus 1690 is used. In thetesting apparatus 1690, the disk of FeRh 1635 is embedded in agarose1680 next to an MM-compatible optical fiber-based thermometer 1681(which can be procured from FISO Technologies, Inc.). The disk 1635 andthe agarose 1680 are held within a container 1682, which is sealed witha cap 1683. The container 1682 is wrapped in tubing 1684 connected to atemperature-controlled water circulating bath in order to sweep andcontrol the temperature of the disk 1635 and its environment aroundphysiologically relevant temperature range (10-55° C.).

The testing apparatus 1690 of FIG. 16 can be used to createrepresentative gradient-echo images of the effect of the mm-scale diskof FeRh 1635 on the surrounding agarose 1680 as the temperature is sweptfrom the antiferromagnetic phase below the transition temperature to theferromagnetic phase above the transition temperature of the FeRhstructure 1635 and then cooled. In order to produce a gradient-echoimage, the testing apparatus 1690 is inserted into a magnet (such as themagnet 120, which in this test case is an MRI magnet). RF pulses andgradient pulses are applied to the entire FeRh structure 1635. Theresonant signal from the surrounding agarose 1680 is detected byinductive detection coils of the magnetic apparatus 105 (which is an MRImachine) in which the apparatus 1690 is placed. The resonant signal isaffected by how magnetic the FeRh structure 1635 is in the middle ofagarose 1680.

These gradient-echo images are shown in FIGS. 17A-17F. These images aretaken while maintaining the magnetic field magnitude at 4.7T. The FeRhstructure 1635 is 99.9% purity FeRh disk having a volume of 1 mm³. Theimages are taken through the center of the disk 1635 at varioustemperatures as the disk 1635 is heated and then cooled. In each of theimages, a stable image feature 1781 is visible. This feature 1781 isproduced by the thermometer 1681 next to the FeRh disk 1635. Thethermometer 1681 is non-magnetic, and thus, it does not exhibit anyappreciable change in the images as the magnetic field changes (due tothe change in the temperature) from FIG. 17A to FIG. 17F. The feature1781 is difficult to see in FIGS. 17C and 17D (but it is labeled to showits location) because the signal from the FeRh disk 1635 overwhelms it.FIG. 17G shows a width of the MRI signal 1782 (or image artifact)created by signal loss due to the magnetic field gradients from the FeRhdisk 1635 as a function of the set-up temperature.

Specifically, FIGS. 17A-17F show six representative gradient-echo images(out of 52) of the effect of the FeRh mm-scale disk 1635 on thesurrounding agarose 1680 as the temperature of the set-up is sweptthrough physiologically relevant temperature range (10-55° C.) at theconstant MRI magnetic field of 4.7 Tesla. The image parameters are asfollows: TR/TE=100/2.2 ms, FA=25 degrees, nominal resolution=0.46×0.46×1mm, FOV=60.0×60.0 mm. In chronological order, FIG. 17A shows thegradient-echo image taken at a temperature of 25° C.; FIG. 17B shows thegradient-echo image taken at a temperature of 45° C.; FIG. 17C shows thegradient-echo image taken at a temperature of 45° C.; FIG. 17D shows thegradient-echo image taken at a temperature of 35° C.; FIG. 17E shows thegradient-echo image taken at a temperature of 30° C.; and FIG. 17F showsthe gradient-echo image taken at a temperature of 26° C.

The demonstrated agarose image phase shift with concomitant magneticfield change emanating from the magnetocaloric FeRh disk 1635 is seen inthe increase of the MM signal 1782 around the sample in FIGS. 17A-17F.As the magnetization data of FIG. 14B dictates, the temperature increasedrives the FeRh disk 1635 to transition from the low-momentantiferromagnetic phase below the transition temperature to thehigh-moment ferromagnetic phase above the transition temperature andthen back to the low-moment antiferromagnetic phase as the FeRh disk1635 is cooled. When the magnetically manipulatable material 1635 goesto a magnetic state (for example, increasing temperature for FeRh) froma non-magnetic state, the surrounding substance (for example, agarose1680), that is, the substance around the magnetically manipulatablematerial 1635, sees both the background magnetic field produced by themagnet 920 and the magnetic field produced from the now-magneticmaterial (in this example, the FeRh in the disk 1635). That extra fieldfrom the FeRh disk 1635 is non-uniform and in essence alters the MRIsignal 1782 around the FeRh to some distance, it puts it out ofdetection range. This is why the gradient-echo image looks much largerand darker as the magnetic field increases. It is not that the FeRh disk1635 is any bigger, it is that the FeRh disk 1635 changes its magneticstate, which in turn changes the MRI signal of the surrounding substance1680 and makes the image change to a larger darker spot.

Loss of signal in the MM of FIGS. 17A-17F due to the changing magneticstate of the magnetocaloric material closely follows the magneticproperties that are shown in FIG. 14B. The size of the region withsignal dropout due to the high magnetic field gradients approximatelydoubles in each dimension, a factor of 8 in volume. This effect isplotted in FIG. 17G, which shows the MM signal loss region size (in alinear dimension) as a function of temperature. The image parameters areas follows: TR/TE=100/2.2 ms, FA=25 degrees, nominalresolution=0.46×0.46×1 mm, FOV=60.0×60.0 mm.

The clearly demonstrated phase shift with concomitant magnetic fieldchange is seen in the increase of the MRI signal void. There was alarger hysteresis and lower apparent moment increase in the MM data thanin the magnetometer data, which may be related to mechanical stress whencutting the material (the FeRh disk 1635) to a smaller size. Thishysteresis effect could be viewed as a benefit, in that once a particlein the FeRh disk 1635 is turned “on” then it will remain on untilremoved from the field.

In general, this result can be assumed to apply for the magnetocaloricmaterials in the structure 135 when it is placed in the magnet 120. Whenthe magnetocaloric material is in a non-magnetic state (for example, ata low temperature for FeRh or at a high temperature for La—Fe—Si), thewater surrounding the structure 135 experiences just the MRI magneticfield supplied by the magnet 120 on the order of Tesla (depending on thescanner magnetic field). But when the magnetocaloric material goes to amagnetic state (for example, at a high temperature for FeRh or at a lowtemperature for La—Fe—Si), the water around the structure 135experiences both the MRI scanner magnetic field (from the magnet 120)and the magnetic field from the now magnetic magnetocaloric material inthe structure 135. That extra field from the magnetic magnetocaloricmaterial is non-uniform and in essence alters the MM water signal aroundthe structure 135 to some distance, it puts it out of detection range.

Switching protocols for using FeRh as the magnetically manipulatablestructure 135 are discussed next with reference to FIGS. 18A-18C. Aswitching protocol describes the transition of the magnetocaloricmaterial in the structure 135 from the first magnetic state to thesecond magnetic state. FIG. 18A shows the MRI magnetic field at thevalue where the center of the first order magnetic phase transition ofthe magnetocaloric material is at the physiological temperature of 37°C. Temporary heating and cooling switches the magnetocaloric materialbetween the MRI visible (ON) and invisible (OFF) states. FIG. 18B showsthe MRI magnetic field is at the value where the center temperature ofthe magnetocaloric material first order magnetic phase transition ishigher than the physiological temperature of 37° C. Temporary heatingswitches the magnetocaloric material to the MM visible (ON) state whilethermal relaxation to equilibrium temperature brings the magnetocaloricmaterial back to the MM invisible (OFF) state. FIG. 18C shows themultiplexing of two magnetocaloric materials that have phase transitionsat two different magnetic field values at the physiological temperature.The two magnetocaloric materials are visible or invisible at differentmagnetic fields and can therefore be differentiated in images fromdifferent MRI scanners (in this example at 1T, 4T, and 7T).

As discussed above, FeRh is a suitable switchable and tunablemagnetocaloric material in the typical MM settings (Tesla-scale magneticfields) and in-vivo physiological temperatures (around 37° C.) through avery sharp first order magnetic phase transition. FeRh is only one in alarge repertoire of magnetocaloric materials that have similar switchingcharacteristics under similar environmental conditions, where sharpfirst order magnetic phase transition with a positive M vs. T slope isobserved at physiological temperatures and Tesla-scale magnetic fields.Furthermore, there are many magnetocaloric materials where the sharpfirst-order magnetic phase transitions can also have a negative M vs. Tslope at physiological temperatures and Tesla-scale fields, or even acombination of sharp positive and negative slopes, making magnetocaloriccompounds even stronger candidates as versatile materials for highdifferential contrast switchable MM labels.

The switching protocols can be used for in-vivo MM settings. The MRIcontrast agent using FeRh can be reversibly switched by thermal cyclingof the entire sample set-up over the physiologically relevanttemperature range. Other potential engineering solutions tomagnetocaloric MRI label switching include heating by MRI compatiblefocused ultrasound or high-frequency inductive heating, cooling by MRIcompatible thermo-electric coolers, or magnetocaloric material switchingby adding or subtracting to the main magnetic field of the MRI (in thesimplest version this can be accomplished by temporarily removing thesample from the MRI bore).

When considering such MRI label switching solutions, magneto-thermalproperties of the magnetocaloric material are also considered,especially the location of the first order magnetic phase transition ofthe magnetocaloric material. FIGS. 18A-18C schematically describespecific examples. In FIG. 18A, the MM label has two stable magneticstates (indicated by the solid black dots) at 37° C. (310K). Thisexample is well represented by the 99.9% purity FeRh magnetocaloricmaterial at 5 Tesla, as shown in FIG. 14B. In the low magnetic momentstate the magnetocaloric material is MRI invisible (Label OFF). Themagnetocaloric material can be switched on by temporarily raising itstemperature by few degrees C. (approximately ΔT=5° C. for our 99.9%purity FeRh magnetocaloric material at 5 Tesla shown in FIG. 14B)through application of a heating pulse (by any of the above listedpotential methods). Once the magnetocaloric material is thermallyrelaxed back to the equilibrium temperature of 37° C., it remains in thehigh magnetic moment state and is MRI visible (Label ON). It can beswitched off again by active cooling where the temperature of themagnetocaloric material is temporarily lowered. Once the magnetocaloricmaterial relaxes back to the equilibrium temperature of 37° C., it willbe in the low magnetic moment state and again MRI invisible (Label OFF).This is also the procedure performed for obtaining the gradient-echoimages as described in FIGS. 17A-17F.

The second possibility is described in FIG. 18B. In this case themagnetocaloric material has only one stable magnetic state (indicated bythe solid black dot) at 37° C. (310K). This example is well representedby 99.9% purity FeRh magnetocaloric material at 3 Tesla, as shown inFIG. 14B. In this low magnetic moment state the magnetocaloric materialis MRI invisible (Label OFF). The magnetocaloric material can betemporarily switched on by raising its temperature through applicationof a larger heat pulse than was described in FIG. 18A since highertemperature change is required to take the magnetocaloric materialthrough the first order magnetic phase transition (In the case of our99.9% purity FeRh at 3T as shown in FIG. 14B, it would takeapproximately ΔT=20° C. to switch the magnetocaloric material). Themagnetocaloric material remains MRI visible (Label ON) in the highmagnetic moment state as long as the temperature of the magnetocaloricmaterial is above the phase transition temperature. As themagnetocaloric material thermally relaxes back to the equilibriumtemperature of 37° C., it automatically goes back through the phasetransition into a low magnetic moment state and becomes MM invisibleagain (Label OFF). The advantage of this configuration is that activecooling is not required for switching the magnetocaloric material intothe MM invisible OFF state, while the disadvantage is that the highertemperature increase is required to temporarily switch the label intothe MM visible ON state.

Another feature of MRI switchable labels brought about by the variety ofmagneto-thermal properties of magnetocaloric materials is thepossibility of multiplexed labels made MRI visible or invisible atdifferent magnetic field or temperature values by appropriate materialsscience design. FIG. 18C describes the possibility of two switchable MRIlabels that can be differentiated in images from MRI scanners operatingat different magnetic field values. Label 1 has a first order magneticphase transition at 2 Tesla and is well represented by the 99% purityFeRh magnetocaloric material at 27° C. (300K) shown in FIG. 15A. Label 2has a first order magnetic phase transition at 6 Tesla and is wellrepresented by the 99.9% purity FeRh magnetocaloric material at 27° C.(300K) shown in FIG. 15B. In a 1T MRI scanner, both of these labelswould be in the low magnetic moment state below their respective firstorder magnetic phase transition temperatures and therefore invisible inthe MM (both labels OFF). In a 4T MRI scanner, Label 1 would be in thehigh magnetic moment state above its magnetic phase transitiontemperature and therefore MM visible (Label 1 ON), while Label 2 wouldstill be in the low magnetic moment state below its magnetic phasetransition temperature and therefore still MRI invisible (Label 2 OFF).Finally, in a 7T MM scanner, both of these labels would be in the highmagnetic moment states above their respective magnetic phase transitiontemperatures and therefore MM visible (both labels ON). Images fromthese MM scanners with different operating DC magnetic fields wouldreadily differentiate the two labels.

Referring to FIGS. 19A and 19B, two different magnetically manipulatablematerials are shown that function similarly to the examples shown inFIGS. 6A and 6B, respectively. In FIG. 19A, the magneticallymanipulatable material is Fe—La—Si, while in FIG. 19B, the magneticallymanipulatable material is 99% purity FeRh. FIG. 19A is a graph of themagnetic state of Fe—La—Si versus temperature T within the sample 115,while maintaining the sample 115 at a constant magnetic field of 1 T. Asshown in this graph, Fe—La—Si transitions from a magnetic to anon-magnetic state with a rise in the temperature T. FIG. 19B is a graphof the magnetic state of 99% purity FeRh versus temperature T within thesample 115, while maintaining the sample 115 at a constant magneticfield of 1 T. As shown in this graph, FeRh transitions from anon-magnetic to a magnetic state with a rise in the temperature T.

Referring to FIG. 20, a procedure 2000 is performed by the apparatus 200for using the magnetic apparatus 205 and the magnetically manipulatablestructure 235 to control, alter, or operate on the sample 215. Forexample, the structure 235 can include the magnetically manipulatablematerials 236, the magnetic apparatus 205 can be an MM machine, and thematerials 236 can act as one or more tunable and switchable labels inthe MRI machine 205.

The procedure 2000 includes receiving the sample 215 in the samplevolume 210 defined by the magnetic apparatus 205 and the magnet 220(2005). The sample 215 can be placed inside the magnet 220 using anysuitable technique that is used in MRI machines. The sample 215 can be awhole living organism, or it can be a portion or a region of a livingorganism. The magnetically manipulatable structure 235 and the material236 are prepared within the sample 215 (2010). For example, thestructure 235 can be embedded within the sample 215 using the injectionapparatus 260 and this can occur prior to or after the sample 215 isplaced inside the magnet 220.

The magnetic field having the magnitude B is created in the sample 215(2015). For example, the control system 240 can send a signal to theenergy supply 225 to provide current to the electrically conductive wirecoils of the magnet 220. The magnitude B of the magnetic field isgenerally greater than 0.5 Tesla and can be in a range of 1-20 Tesla.

A property associated with the sample 215 is changed while generallymaintaining the magnetic field magnitude B constant in the sample 215(2020). The property that is changed (2020) can be the magnetic field ora temperature or both the magnetic field and the temperature of thesample 215. If the property that is changed is the magnetic field, thenthe change in the magnetic field is substantially smaller than themagnitude B of the field that is held constant. The change in magneticfield is at least an order of magnitude smaller than the magnitude B.Similarly, if the overall temperature of the sample 215 is between about270-370 K, and the property to be changed (2020) is the temperature,then the change in the temperature is substantially less than theoverall temperature of the sample 215. For example, the temperaturechange can be about 10-40 K. The change in the property (2020) can beaffected by the sample property scanning system 245, as discussed above.

Because the magnetically manipulatable structure 235 includesmagnetically manipulatable materials 236, the change in the property(2020) causes the magnetically manipulatable materials 236 to transitionfrom a first magnetic state to a second magnetic state, and thistransition causes a change in the sample 215 near to the structure 235.This change in the sample 215 is detected (2025). This means that thestructure 235 can be turned on and off by the procedure 2000 and has theeffect that it can be used as a high-contrast tunable and switchablelabel for MRI machines 205. The structure 235 can therefore be used asan MRI contrast agent or a sensor because of these properties. Thus, thechange in the magnetization of the magnetically manipulatable materials236 of the structure 235 can be detected by the apparatus 200 byobserving the effect the change has on the water or biological tissuesurrounding the materials 236.

Referring to FIG. 21, a procedure 2100 is performed by the apparatus 900for actuating (for example, activating and de-activating) a biologicalconstruct (which can be the thermally-sensitive biological construct930) within a sample 915. The sample 915 is received in the actuationvolume 910 defined by the magnet 920 of the magnetic apparatus 905(2105). The magnetically manipulatable structure 935 is physically (forexample, thermally) coupled with the biological construct within thesample 915 (2110) such that the biological construct changes its statusin response to a change in property of the magnetically manipulatablestructure 935. Thus, if the physical coupling is a thermal coupling andthe biological construct is a thermally-sensitive biological construct930, then the thermally-sensitive biological construct 930 changes itsstatus in response to a change in a temperature of the magneticallymanipulatable structure 935.

The magnetic field having the magnitude B is created in the sample 915(2115). For example, the control system 940 can send a signal to theenergy supply 925 to provide current to the electrically conductive wirecoils of the magnet 920. The magnitude B of the magnetic field isgenerally greater than 0.5 Tesla and can be in a range of 1-20 Tesla.

A characteristic within the sample 915 is changed (2120) For example,the characteristic of the sample 915 that is changed (2120) is themagnetic field within the sample, 915. The magnetic field within thesample 915 can be changed by changing a DC current supplied to themagnet 920. The change in the magnetic field is substantially smallerthan the magnitude B of the field that is held constant. The change inmagnetic field is at least an order of magnitude smaller than themagnitude B. The change in the characteristic within the sample 915(2120) can be affected by the sample property scanning system 245, asdiscussed above.

The change in the characteristic (such as the magnetic field) (2120)causes the property (such as the temperature) of the magneticallymanipulatable material 936 i to change, and this causes a change in astatus of the biological construct (2125). The change to the status ofthe biological construct (2125) can occur without causing a change inthe status of other materials within the sample 915. For example, thechange in the magnetic field (212) causes a change in the temperature ofthe magnetically manipulatable material 936 i, and this causes a changein the status of the thermally-sensitive biological construct 930.

What is claimed is:
 1. An imaging apparatus for imaging a sample, theapparatus comprising: a magnetic apparatus that defines a sample volumethat is large enough to accommodate the sample to be imaged, themagnetic apparatus including a magnet that is configured to create amagnetic field having a magnitude B in the sample; and one or moremagnetically manipulatable materials within the sample, eachmagnetically manipulatable material being a material that exhibits atransition between a first magnetic state and a second magnetic state inresponse to a change in a property associated with the sample while themagnetic field having the magnitude B is maintained in the sample. 2.The imaging apparatus of claim 1, further comprising an energy supplyconnected to the magnet, wherein the magnet includes electricallyconductive wire coils through which current from the energy supply ispassed, wherein the energy supply provides a DC current supplied to thewire coils.
 3. The imaging apparatus of claim 2, wherein the magnet is asuperconducting magnet.
 4. The imaging apparatus of claim 1, wherein themagnetic field magnitude B is greater than 0.5 Tesla or in a range of1-20 Tesla.
 5. The imaging apparatus of claim 1, wherein the firstmagnetic state is an antiferromagnetic state or a paramagnetic state,and the second magnetic state is a ferromagnetic state or aferrimagnetic state.
 6. The imaging apparatus of claim 1, wherein theproperty associated with the sample is a temperature, and the transitionoccurs in response to a change in temperature less than 20 K.
 7. Theimaging apparatus of claim 1, further comprising a sample propertyscanning system configured to change the property of the sample whilethe magnetic field having magnitude B is maintained in the sample. 8.The imaging apparatus of claim 1, wherein the property associated withthe sample is a magnetic field, and the transition occurs in response toa change in a magnitude of a magnetic field that is substantiallysmaller than the magnitude B.
 9. The imaging apparatus of claim 1,wherein the magnetic apparatus is a magnetic resonance imagingapparatus.
 10. The imaging apparatus of claim 1, wherein themagnetically manipulatable material is a magnetocaloric material. 11.The imaging apparatus of claim 1, wherein the magnetically manipulatablematerial is a material selected from the group consisting ofiron-rhodium, alloys of iron-rhodium, alloys of manganese arsenide,Heusler alloys, and alloys of manganese-iron.
 12. The imaging apparatusof claim 1, wherein the sample is a living organism and the sample isheld at a physiological temperature to maintain the organism in a livingstate.
 13. The imaging apparatus of claim 1, further comprising adetector that detects a signal produced as a result of the interactionbetween the magnetic field and the sample.
 14. The imaging apparatus ofclaim 13, further comprising a control system connected to the magneticapparatus, wherein the control system is configured to: receive dataoutput from the detector, the output relating to the detected signal,analyze the received data, and estimate the sample property based on theanalysis.
 15. The imaging apparatus of claim 1, wherein eachmagnetically manipulatable material is in the form of a plurality ofspatially-separated particles, wherein the particles are dispersedthroughout at least one region of interest within the sample.
 16. Theimaging apparatus of claim 15, wherein the size of the particles is onthe order of the size of cells within a sample that is a livingorganism.
 17. The imaging apparatus of claim 1, wherein the magneticallymanipulatable material remains magnetically unsaturated while themagnetic field having the magnitude B exists in the sample.
 18. Theimaging apparatus of claim 1, wherein the one or more magneticallymanipulatable materials comprises a plurality of magneticallymanipulatable materials, with each magnetically manipulatable materialhaving a transition that occurs in response to a distinct change in theproperty of the sample.
 19. The imaging apparatus of claim 18, wherein:a first of the magnetically manipulatable materials has a transitionfrom the first magnetic state to the second magnetic state that occursin response to an increase in the sample property; and a second of themagnetically manipulatable materials has a transition from the firstmagnetic state to the second magnetic state that occurs in response to adecrease in the sample property.
 20. The imaging apparatus of claim 18,wherein: a first of the magnetically manipulatable materials has atransition from the first magnetic state to the second magnetic statethat occurs in response to an increase in the sample property; and asecond of the magnetically manipulatable materials has a transition fromthe second magnetic state to the first magnetic state that occurs inresponse to an increase in the sample property.
 21. The imagingapparatus of claim 18, wherein: a first of the magneticallymanipulatable materials has a transition between the first magneticstate and the second magnetic state that occurs in response to a changein a first sample property; and a second of the magneticallymanipulatable materials has a transition between the first magneticstate and the second magnetic state that occurs in response to a changein a second sample property that is distinct from the first sampleproperty.
 22. The imaging apparatus of claim 1, wherein: the transitionfrom the first magnetic state to the second magnetic state occurs in afirst range of values of the property as the property is increased; thetransition from the second magnetic state to the first magnetic stateoccurs in a second range of values of the property as the property isdecreased; and the first range of values is distinct from the secondrange of values.
 23. A method comprising: receiving a sample in a samplevolume defined by a magnetic apparatus; preparing at least onemagnetically manipulatable material within the sample; creating amagnetic field having a magnitude B in the sample; changing a propertyassociated with the sample while maintaining the magnetic field havingthe magnitude B in the sample; and detecting a transition between afirst magnetic state and a second magnetic state of a magneticallymanipulatable material in the sample in response to the changingproperty associated with the sample.
 24. The method of claim 23, whereinchanging the property associated with the sample comprises changing atemperature in the sample in a range that is less than 20 K.
 25. Themethod of claim 23, wherein changing the property associated with thesample comprises changing a magnetic field in the sample in a range thatis substantially smaller than the magnitude B.